Duravit Metro flush valve leak

Hi everyone. I have an 8 year old Duravit Metro, and right now every 5 minutes or so the water level drops a tad (like 1 cm or so) and triggers the tank to refill back to the fill line. Suspecting that this was a flush valve issue, I purchased and installed a new one (Flush valve 2" for Metro, part #0074135300). First, I cleaned the area of the bottom of the tank where the flush valve mounts and the gasket forms a seal. After installing, I added a bit of water and confirmed after waiting several hours that the seal at the gasket (not at the flapper) is water tight. However, in full operation the toilet is doing the same thing again! This is an entirely brand new flush valve. Is this just a design flaw with regard to how the flapper mechanism on the Duravit Metro works?

Is there anything else that I should check before considering purchasing a new, more reliable toilet? Thanks.

I was suggesting to clean and inspect the seat. However I now see that included a whole new seat.

Hmmm.. Tighten it more? Maybe somebody will recommend a compound or grease or pipe dope to put on the gasket. Your test with shallow water may not show a leak that would occur when the water is higher.

Thanks for the quick response. Yes, I can try going tighter with the entire mount, but my experience with reef aquarium plumbing is that tighter (beyond some point) isn't necessarily better when it comes to gaskets and sufficiently good seals. The one thing on this part is that the seal made by the flapper consists of little more than a white, rubber o-ring. And the flapper itself isn't all that heavy. So I wonder, if sometimes after a flush that the flapper might not close down hard enough. In such a case, a trickle could slip around the o-ring if the flapper closes "lightly".

Actually, changing just the flapper wouldln't have made any difference, given that the same problem persists after a wholesale replacement of the flush valve + flapper. But you are right -- that would've saved me $20 or so. Also, I did confirm that the refill hose is mounted properly and is short enough such that there is no chance of a reverse siphon forming.

Also, in doing reef aquarium plumbing, do you commonly put some silicone grease on O-rings?

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Typically, no. They recommend not using silicone grease or any other lubricants when installing bulkheads because such materials can cause the rubber gasket to squish or scoot and create an uneven seating. Tight is good, but within reason -- the issue being that overly tight can stress glass or acrylic.

These are very simple systems that seem complex when they act up and behave in mystifying ways. However, all you've got is a tank of water and a device that keeps the water in. Water is running out, so let's see what's causing it.

Presumably, you would notice if the water was overflowing the top of the overflow riser, so I'm assuming it isn't your water level setting.

I also assume that, if you turn off the water to the toilet, it will drain down substantially. So you have water leaking out. It's either a crack in the valve or a flapper that isn't seating properly. Check to see that the chain has just a little slack when the flapper is seated. Check that the trip handle is pulling it straight up rather than to the side; it may not reseat properly if it's pulled to the side. If your flush valve is properly-seated and not leaking and not cracked, and it's not the refill hose, then it's a matter of how the flapper is sealing against the flush valve seat. It is either being held off by the chain (or by something non-obvious like the cover pushing down slightly on the trip lever when reinstalled -- something that happens on my old AS toilet), finding an irregular surface to bond against, or not sitting straight down. All should be readily-fixable. Try pushing on the flapper to see if you can make it seal.

These aren't going to be high-volume parts, so it's possible that your new flapper is deteriorated. However, I'm guessing it's just an install issue of some kind. You might also call Korky at 1-800-LAVELLE and ask them if they have a flapper that is appropriate for your toilet and try that on your flush valve.